Chemistry Practice Test for the HESI® exam
Using the Lewis-dot structure model, how many dots would carbon have?
The number of dots in a Lewis-dot structure model corresponds to the number of valance electrons for that atom. Because carbon has four valance electrons, it’s Lewis-dot structure model would have 4 dots.
Which of the following would produce Hydrogen ions in an aqueous solution and would turn a litmus test from blue to red?
Blue litmus paper turns red in the presence of an acid. Ammonia, lye, and detergent are basic, so they would not give off Hydrogen ions in an aqueous solution and when added to blue litmus paper the paper would remain blue.
Dihydrogen monoxide is better known as what?
Dihydrogen monoxide, or H2O, is more commonly known as water.
What is the most abundant element in Earth’s crust?
Oxygen makes up about 47% of the Earth’s mass, followed by Silicon at 28%, Aluminum at 8%, Iron at 5%, Calcium at 4%, and Sodium and Potassium, each at 3%.
What is the most abundant element in the universe?
Hydrogen is the most abundant element in the universe, followed by Helium and then Oxygen.
Which one of the following elements is liquid at room temperature?
Mercury is the only element that is liquid at room temperature.
A solution that contains the maximum amount of dissolved solute is said to be what?
A saturated solution is one that has the maximum amount of solvent dissolved into it.
The change in state from a gas to liquid is called what?
Condensation is the reverse of vaporization and can be observed when gas cools and becomes a liquid, such as when dew appears in the morning after the temperature drops at night.
Which of the following is not a property of water?
This is the only answer choice that is not true, as the question asks. Ice, the solid form of water, is less dense than the liquid form, which is why ice floats in water.
Viscosity increases in what circumstance?
Viscosity, or the resistance of a fluid against force, increases with a temperature decrease, that is, fluid becomes more viscous (flows slower) in colder temperatures.
Which of the following is true of gas particles?
Gas particles exert little to no force on each other, so they “bounce” off each other when they collide. The other options are all false regarding gas particles
Reactions that absorb heat are called what?
Endothermic reactions absorb heat, while exothermic reactions give off heat.
What is the molar mass of Calcium if its atomic mass is 40 amu?
The molar mass of an element is essentially the same as its atomic mass.
What is the name of NO 2
“N” is representative of Nitrogen in the periodic table, and “O” is representative of Oxygen. Oxides are compounds with at least one oxygen atom and another different type of atom (e.g., Nitrogen). The “2” behind the “O” changes the prefix to “di”, which has its roots in Greek and means “two” or “twice.”
BF3 is also known as what?
“B” is representative of Boron in the periodic table, and “F” stands for Fluorine. Anions of the element Fluorine are called Fluorides. The “3” behind the “F” changes the prefix to “tri,” making the correct answer “Boron trifluoride.”
In the formula C12H22O11 the 12 in front of the carbon represents indicates 12 “what” of carbon?
The number that comes after an element in a formula represents the number of those atoms found in that substance.
In an ionic bond, a positively charged ion is attracted to what type of ion?
Ionic bonds involve attraction between oppositely charged ions, so a positively charged ion would be attracted to a negatively charged ion, also called an anion.
High density matter which is little affected by pressure and holds its shape is classified as which of the following?
Gases, plasma, and liquids do not have some or all of these properties.
DNA & RNA contain many of the same nitrogen-containing bases. Which base is only found in RNA?
The bases of DNA are adenine, thymine, cytosine, and guanine, whereas the bases of RNA are adenine, uracil, cytosine, and guanine.
Which of the following is not a component of lipids?
Chemically speaking, lipids are composed of primarily of carbon, hydrogen, and oxygen.
Simple carbohydrates composed of a single ring are also called what?
Monosaccharides are the most basic, singular unit of carbohydrates. If you did not know this, it may help to know that the pre-fix “mono” means “one.”
Which of the following is a water-soluble vitamin?
B and C vitamins are soluble, meaning they are not stored by the body and must be replaced each day.
A catalyst increases which of the following in a chemical reaction?
A catalyst lowers the amount of energy needed in a reaction, thus increasing the speed. They are not used up in the reaction and are only needed in small amounts.
The vertical columns of the periodic table are called what?
In the periodic table, vertical columns are called groups, and the horizontal rows are called periods.
Bleaches, disinfectants, & salts often contain elements from which nonmetal group?
The halogens are a group on the periodic table that are toxic and include Fluorine, Chloride, Bromine, Iodine, and Astatine.
Which is not a property of metals?
Metal has a high density and melting point, is malleable, and is an excellent conductor of heat.
The breakdown of which of the following provides the energy needed for chemical reactions in the body?
ATP is found in all living cells and is obtained from the breakdown of food.
A particle with a negative or positive charge is referred to as what?
Ions have a different number of electrons and protons, which makes them have either a positive or negative charge.
The bond between water molecules is called what?
The hydrogen bond between water molecules is responsible for its high boiling point
Which pH would be the most basic?
The pH scale ranges from 0-14, with 0 being the most acidic, 7 being neutral, and 14 the most basic.
Positively charged particles in an atom are called what?
Protons have a positive charge, electrons have a negative charge, and neutrons have a neutral (no) charge
The chemical 4[NH4(SO4)2⋅12H]contains how many more hydrogen atoms than oxygen atoms?
Use the given chemical formula to compute the total number of hydrogen atoms and the total number of oxygen atoms. Subscripts attached to an atom in a chemical formula indicate the number of that particular atom. Subscripts attached to a molecule indicate the number of that particular molecule. Coefficients also indicate the number of a particular atom or molecule. The NH4 indicates that there are 4 hydrogen atoms per NH4molecule. The coefficient of 4 indicates that there are 4⋅4=16 hydrogen atoms coming from the NH4. This also applies to the 12Hto give 4⋅12=48 hydrogen atoms. Combining these, there are a total of 64 hydrogen atoms in the chemical. Apply the same technique to find the total number of oxygen atoms: the SO4 shows that there are 4 oxygen atoms per SO4 molecule, and 2 of each of these molecules to give 4⋅2=84⋅2=8 oxygen atoms. This is multiplied with the coefficient 4 to give a total of 8⋅4=328⋅4=32 oxygen atoms. Finding the difference: 64−32=32
Which of the following is a polar molecule?
Polarity in molecules arises from the separation of charge within a molecule. This charge separation results from differences in the electronegativity of bonded atoms. Atoms which are more electronegative pull electrons more strongly than less electronegative atoms, and in so doing create a partial negative charge where the electron density is high and a partial positive charge where the electron density is low. This separation of charge produces an electric dipole which can then interact with other charged atoms or molecules. In cases where electronegativity values are not provided (meaning the bond cannot be classified as polar or nonpolar), the symmetry, or lack thereof, in a molecule can be used to classify it as polar. BF3 exhibits three equal bonds equally separated, so even though each BF bond is polar, the equal number and equal separation results in an overall nonpolar molecule; this is due to vector addition. Similarly, CO2, though containing individual polar bonds is overall nonpolar because of symmetry. C6H6 contains symmetry, but CH bonds are nonpolar. NH3 is polar because of asymmetry and the lone pair of electrons held by the nitrogen atom.
An unknown element has a mass number of 33 and an atomic number of 12. How many neutrons does the element contain?
The mass number of an atom provides the total number of neutrons and protons in the atom. Electrons, which are incredibly light, do not significantly contribute to the overall mass of an atom; recalling this fact can make it easier to remember the meaning of the mass number. An atom’s atomic number represents the total number of protons in the atom. The number of neutrons can then be found by calculating the difference between the mass number and the atomic number: 33−12=21
Rank the following intermolecular forces in increasing strength: hydrogen bonding, London dispersion forces, ion-dipole interactions, ion bonding, and dipole-dipole interactions.
Intermolecular forces are those acting between individual molecules. As these forces primarily result from differences in electric charges, the forces associated with the largest charge density will be the strongest. Ions, resulting from the gain or loss of an electron, exhibit a “full” positive or negative charge. Consequently, bonds resulting from their interaction exhibits the greatest strength of the interactions presented here. Dipoles, which result from intramolecular charge separation due to differences in electronegativity, are not as electronically dense as ions, but still show a partial charge. Hydrogen bonding is a specific type of dipole-dipole interaction, which is particularly strong due to the electronegativity of those atoms bonding to the hydrogen (nitrogen, oxygen, or fluorine); hydrogen bonding is a strong type of dipole-dipole interaction. London dispersion forces are those exhibited between nonpolar molecules resulting from the interactions of the fluctuating charge-density in any molecule. The slight positive and negative charges produced during the motion of electrons enables very weak attractions between atomic nuclei to form.
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